It may not be nice to trick Mother Nature, but that's exactly what George Seidel has figured out how to do. Seidel and his colleagues have discovered the key to choosing the gender of new life. They can now dictate with 90 percent accuracy whether or not a calf will be a heifer (female) or a bull (male).
By sexing sperm, or sorting it by gender, animals can be artificially inseminated to bear one sex or the other depending on a producer's needs. When applied to livestock, this discovery gives producers an enormous edge. For example, a dairy farmer can ensure heifer calves, giving him more future milk cows for his herd.
"Sperm come with either an X or a Y chromosome. Eggs only come with an X chromosome," explains Seidel. "When life is conceived and those chromosomes merge, it's either XX for female or XY for male."
Most animals produce an equal number of X and Y sperm, creating a 50-50 chance for each gender to be conceived. Seidel says X sperm are minutely bigger, but it is a very slight difference.
"If you think about it, you want the X and Y sperm to be the same because if one was much bigger than the other, it would be much slower. A slower sperm would have less chance of fertilizing an egg, so you wouldn't get a 50-50 mix of each gender in the population," says Seidel. "Nature goes to great lengths to make sure they are as identical as possible, which makes it very difficult to tell one from the other."
But by a fluke, the U.S. Department of Energy discovered a way. Scientists in the nation's top weapons lab in California routinely monitor the health of their employees, who are exposed to radiation, lasers, and bombs. Typical checks include drawing blood, but technicians worried about the cells of the next generation the children of their employees. How would their parent's work environment and exposures affect them? As a result, the technicians started collecting sperm. Their high-tech equipment allowed them to look at the sperm in detail, and they discovered that there were two kinds: male and female.
Eventually, the Department of Energy and the U.S. Department of Agriculture started working together to apply this finding to farm animals. They learned to sort male sperm from female, but their early methods were harsh and killed the sperm. Eventually, they discovered the more effective method of dying the sperm and passing them through a laser. Female sperm contains about 4 percent more DNA, making the dye slightly brighter under the laser.
But even after several years of refining the technique, sorting is still a slow process. The present process can sort about 1,500 sperm of each sex per second, a drastic improvement over the earliest tries, which could only sort 100. But traditional artificial insemination requires millions of sperm to ensure conception; for pigs, it requires billions. At that rate, says Seidel, it can take days to sort enough sperm to impregnate one animal, and sperm is hard to keep alive outside of a body.
Clearly, a new strategy was necessary.
"I thought to myself, It only takes one sperm to fertilize an egg. If you do everything just right, maybe you could be successful with fewer sperm,' " says Seidel.
So, Seidel and several other researchers ran a series of experiments to combine the sperm sexing technology with improved artificial insemination technology. "The combined process works very well in some situations," says Seidel. "Our initial pregnancy rate ranged between 0 to 45 percent. Normal rates for artificial insemination is 60 percent. We're now within 10 percent of normal artificial insemination pregnancy rates."
Research shows that animals born of sexed semen are normal, giving producers the edge Seidel was hoping for. Research continues, conducted in part by a private company, XY Inc., based in Fort Collins, formed to make this technology available to producers.
"My objective is to make the use of sexed semen economical and practical for producers," said Seidel. "It can make ranching more efficient and, ultimately, benefit the consumer."
Seidel said he expects the technology will be available to producers by the beginning of 2001.